Your brain alone needs over 100 grams of glucose a day. Then your gut, thyroid, adrenals, gonads, muscles, hair all require glucose too.
Making this glucose from protein is very stressful and slows your metabolism.
Optimal health is when you are eating AND burning lots of carbs

Burning glucose:
- produces more co2
- requires less oxygen
- lowers stress
- improves metabolic rate
- produces fewer reactive oxygen species
It is the most efficient fuel and that is why your brain, gonads, sperm, hair & the most metabolically intesive organs require it

Everybody has been misled about glucose.
Every single disease is correlated with high blood glucose and over the last 50 years we oversimplified this to mean that we just need to cut glucose out of the diet.
But the high glucose in disease is because your body isn't burning it

Stress
Endotoxins
Omega 6 fatty acids
Nutrient deficiencies
Low thyroid
All of these things block glucose oxidation and are the real problem, not the glucose.

When you completely cut out all carbs from your diet it can work usually because you're cutting out loads of other crap...but over time it will backfire. And this is what you see with many people who've done long term keto
Steak + fruit, juice & honey is the optimal diet